B-cell malignancies comprise a heterogeneous group of neoplasms including acute lymphocytic leukemia, chronic lymphocytic leukemia, and B-cell lymphomas. An estimated 65,000 new cases are diagnosed annually in the United States. Current therapeutic strategies can be effective but the majority of patients ultimately relapse and die of their disease. One promising approach for targeting B-cell malignancies involves the cellular immune system through activation of highly efficient T-lymphocytes that mediate key functions such as cytotoxicity, cytokine production, regulation of effector cells, and induction of immunological memory. Earlier clinical studies have shown that dendritic cell vaccination for the priming of naïve T cells can generate tumor-specific CTLs and induce remission in pre-treated patients with human B-cell malignancies. In addition, infusion of HLA-matched allogeneic T lymphocytes has been shown to induce durable long-term remissions in relapsed lymphomas, chronic B-lymphocytic leukemia (CLL), multiple myeloma, or EBV-associated lymphoproliferative disease after stem cell transplantation. However, only a limited percentage of patients with B-cell malignancies will achieve complete remission following donor lymphocyte infusion and the patients are at risk of developing graft-versus-host-disease, which can be associated with significant morbidity and mortality. Therefore, developing peptide-based immunotherapies against specific over-expressed tumor-associated antigens offer an attractive approach for boosting patients' immune system to treat recurrent B-cell malignancies.
CD19, a 95 kDa B lineage-specific transmembrane glycoprotein, functions as a central response regulator in B cells and offers many unique characteristics that make it a relevant target for developing immunotherapeutic strategies. With the important exception of hematopoietic stem cells, CD19 is expressed during all stages of on B cell differentiation, is down regulated on plasma cells,15 and is maintained on cells that have undergone neoplasic transformation. It is expressed on >95% of cells in patients with B cell lymphoma, chronic B-lymphocytic leukemia, and on the acute B-lymphocytic leukemia progenitor cells. The CD19 antigen is also internalized after binding to antibody. Studies have also shown that CD19 expression is maintained despite loss of CD20 expression following treatment with anti-CD20 antibodies.
CD20 is anon-glycosylated 33-37 kDa integral membrane phosphoprotein involved in regulation of B-cell proliferation and differentiation. It is expressed slightly later in B-cell development than CD19, is not rapidly internalized, is expressed at a high surface density on the vast majority of lymphomas, and is eventually down-regulated on terminally differentiated plasma cells. Recently, in the treatment of these cancers, clinical work has focused on passive therapy using rituximab, a monoclonal antibody directed against the CD20 antigen, either alone or coupled to a radioactive compound. Although favorable clinical responses have been observed, these antibodies alone are not curative with most responders achieving only partial remissions with a mean time to disease progression of 13.2 months following antibody treatment.
It is appealing to identify, at a molecular level, the antigens that may be effective immunogens for development of protective immunity against cancer cells. Identifying these antigens would allow vaccination with immunogenic cancer-associated molecules rather than with an uncharacterized mixture of tumor molecules including both immunogenic and immunosuppressive components. Because T cells are critical for the eradication of tumors, it is necessary to understand the nature of the antigens recognized by these cells. CD19 and CD20 are well known as the B cell lymphoma associated surface antigen due to the over-expression on those cells. Monoclonal antibodies to CD20 such as rituximab have been suggested as an effective immunotherapy for B cell lymphomas. However, as set forth above, treatment with rituximab does not result in a cure. Vaccination is an alternative immunotherapeutic approach for the treatment of lymphoma. Peptide vaccines have been the subject of pre-clinical and clinical studies for the treatment of various types of tumors, including melanoma, leukemia, and breast cancer.
There continues to be a strong need for methods of diagnosing and viable treatment regimens for diseases or conditions, such as B cell lymphomas, associated with the expression of CD19 and/or CD20.